I do not remember the book's title nor author however, I do remember the introduction. The introduction was:
"they had eatened of the poison harvest and to the dismay of the king and his men, they had all gone insane. ''partial introduction"

This is a possibility:-

PARADOX-The Air We BREATHE and The Wind and Clouds That Scatters POLLUTANTS and POISONS All Over The WORLD (Jun 16, 2006) by Andrew D. Anderson.

My first and last time seeing this book was in 1998. This was eight years before the publication of Paradox.